1. Field of the Invention
The present invention relates to a carburetor for a stratified scavenging two-cycle engine, which introduces, at first, air in order to exhaust combustion gas with the use of pressure variation in a crank chamber, and thereafter introduces a mixture.
2. Description of the Related Art
Conventionally, there has been known a stratified scavenging two-cycle engine which opens, at first, an exhaust port in order to start exhaustion of combustion chamber after a mixture in a combustion chamber is ignited and exploded so that a piston descends, and then opens an scavenging port so as to introduce a mixture which has been fed in a crank chamber, into the combustion chamber in order to exhaust residual combustion gas, and in which air is at first introduced into the combustion chamber from an air passage so as to exhaust the combustion chamber when the scavenging port is opened, and thereafter the mixture is introduced from the crank chamber into the combustion chamber by way of a scavenging passage.
There has been known, as disclosed in, for example, Japanese Patent Laid-Open No. H09-125966 or Japanese Patent Laid-Open No. H09-287521, the above-mentioned stratified scavenging two-cycle engine in which a throttle valve and an air valve may be simply arranged.
However, the stratified scavenging two-cycle engine as disclosed in the above-mentioned documents, associates the throttle valve with the air valve through the intermediary of a large-sized complicated link mechanism. Japanese Patent Laid-Open No. H10-252565 discloses a stratified scavenging two-cycle engine in which a throttle valve and an air valve are integrally incorporated so that a throttle through-hole and an air through-hole are formed in one cylindrical valve element in a diametrical direction of the latter, and then the valve element is fitted in a single body, the two passages being extended in their parallel parts across the body.
In the stratified scavenging two-cycle engine disclosed in the above-mentioned latter publication, since the throttle valve and the air valve are integrally incorporated with each other, there may be obtained such advantages that they can be fit in a relatively narrow space, and in addition, by appropriately setting diameters of the mixture passage, the throttle through-hole, the air passage and the air through-hole and by appropriately setting phases of the through-holes with respect to the passages, the mixture and the air may be stably controlled at a predetermined flow rate ratio.
However, in the stratified scavenging two-cycle engine as disclosed in the Japanese Patent Laid-Open No. H10-252565, the cylindrical mixture passage and air passage are formed respectively up and down in the cylindrical valve element which is longitudinally fitted in the body so as to be rotatable vertically displaceable.
Accordingly, there have been raised the following problems, that is, since a height which is a sum of values corresponding to the diameters of at least two through-holes, that is, the mixture passage and the air passage and a value corresponding to the thickness of a partition wall partitioning these two through holes is required, miniaturization of the body is difficult, and further, since it is required to form at least two through-holes in each of the valve element and the body, it is difficult to reduce the number of manufacturing steps.